Real-time PCR can be used to detect differences between nucleic acid sequences having substantially identical sequences. Through the use of differentially labeled fluorescent nucleic acid probes, for example one that binds to a wild type sequence and one that binds to a mutant sequence, single nucleotide changes in the human genome can be quickly and reliably detected. This resolving power has been applied to medical diagnostics, where single nucleotide polymorphisms (SNPs), i.e., single base changes found within the coding and/or non-coding sequence of a protein, are correlated to human disease.
However, real-time PCR analysis is highly dependent upon the collection and isolation of high quality samples. Poor sample collection and/or isolation require the use of longer assay conditions and greater amounts of real-time PCR reagents, both of which result in increased costs and reduced productivity. Furthermore, failure of a real-time PCR single nucleotide polymorphism detection assay can result in the need to collect additional samples, causing even greater loss in time and resources.
Accordingly, methods resulting in improved sample collection and isolation, which improve the overall success rate of the assay, reduce the reagents required for the assay, and reduce the need to collect additional samples at later time are highly desirable. Furthermore, methods for performing real-time PCR SNP detection assays with lower amounts of sample material will also reduce the challenges associated with the collection and isolation of high quality samples.
Corneal dystrophy can be an autosomal dominant hereditary disease, which initially presents with blurred vision in the center of a patient's cornea. The blurry vision gradually spreads toward the perimeter of cornea, worsening the patient's vision as they age. There are several types of corneal dystrophy that have been characterized, including Avellino corneal dystrophy (also known as Granular corneal dystrophy, Type2), Granular corneal dystrophy (Type 1), Thiel-Behnke corneal dystrophy, Lattice corneal dystrophy, and Reis-bucklers corneal dystrophy. Corneal dystrophies are known to be caused, at least in some cases, by mutations in the transforming growth factor beta induced (TGFBI, also abbreviated as TGFβI) gene encoding the βIG-H3 protein (also known as TGFBI protein, TGFBIp and keratoepithelin).
Heterozygous patients suffering from Avellino corneal dystrophy have increasing loss in vision with age, becoming severe in the later years of life. Homozygous patients, in contrast, can present with severe to complete loss of vision by six years of age. Avellino corneal dystrophy was first recognized as a distinct type of corneal dystrophy around 1988. Prior to then, it was likely misclassified as Granular corneal dystrophy. Today, Avellino corneal dystrophy is known to be the most common form of stromal corneal dystrophy world-wide. In Korea, Avellino corneal dystrophy is believed to have a prevalence around 1 in 870 people (see Lee, J. H. et al., Ophthalmic Epidemiol., 17:160, 2010; see also Holland, E. J. et al., Ophthalmology, 99:1564, 1992; Kennedy, S. M. et al., Br. J. Ophthalmol., 80:489, 1996; Dolmetsch, A. M. et al., Can. J. Ophthalmol., 31:29, 1996; Afshari, N. A. et al., Arch. Ophthalmol., 119:16, 2001; Stewart, H. S. Hum. Mutat., 14:126, 1999).
Previously, it was discovered that heterozygous individuals (e.g., having one wild type TGFBI allele and one mutant TGFBI allele) were highly susceptible to accelerating loss of vision following LASIK surgery. Notably, two years after surgery increased opacity of the cornea was observed in these patients with increasing aggressiveness, eventually resulting in complete loss of vision (Jun, R. M. et al., Opthalmology, 111:463, 2004). Previously, eye surgery has been performed with an expectation that LASIK or Excimer Laser surgery would get rid of vision blurriness of a patient suffering from corneal dystrophy. For a hypothetical number of three hundred thousand cases of LASIK surgery, 300 people would have lost their vision, based on 1/1000 of minimum estimation of heterozygous patients suffering from Avellino corneal dystrophy. Patients who have undergone LASIK surgery are mainly in their 20's and 30's carrying out productive activities; therefore, their vision loss causes serious troubles in both society and economics.
In addition, after approval of LASIK surgery in year 2000 in USA, African American patients suffering from Avellino corneal dystrophy who underwent LASIK surgery have been found to lose eye sight, which infers that plenty of similar cases might be occurring throughout the world.
Therefore, although accurate diagnosis of Avellino corneal dystrophy is required to prevent the progression of Avellino corneal dystrophy by LASIK surgery, the diagnosis of Avellino corneal dystrophy is just conducted by microscopic observation (e.g., slit-lamp examination) of corneal opacity and thus often doctors miss latent symptoms of patients to perform LASIK surgery, which results in vision loss. Therefore, rapid and precise genetic diagnosis of corneal dystrophy is desirable.
A DNA chip for detecting a mutation in TGFBI gene, which is responsible for Avellino corneal dystrophy, was developed (Korean Patent Laid-Open Publication No. 10-2007-0076532). However, the diagnosis of Avellino corneal dystrophy using said DNA chip disadvantageously require several steps, including a step of amplifying DNA in a sample, a step of hybridizing the amplified DNA with the DNA chip, a step of washing the hybridized DNA chip, and a step of detecting a positive response, which can be slow and contribute to errors.
Given the above background, what is needed in the art are improved methods for the collection of biological samples from patients, the extraction of genomic DNA from these samples, and the detection of Avellino corneal dystrophy-related SNPs therefrom.